My invention comprises improvements in a multiple-ratio, automotive vehicle transmission of the kind disclosed in U.S. Pat. No. 4,978,328, which is assigned to the assignee of my invention. That transmission comprises a pair of planetary gear units mounted on an output shaft axis and a hydrokinetic torque converter mounted on the axis of the crankshaft of an internal combustion engine arranged in parallel disposition with respect to the output shaft axis. The turbine of the torque converter is connected to torque input clutches by means of a torque transfer drive between the engine crankshaft axis and the output shaft axis.
The clutches that control the torque flow paths in the planetary gear units during operation in each of four forward driving ratios include a pair of overrunning clutches located between the torque input shaft and torque input elements of the planetary gearing. One overrunning clutch is adapted for torque delivery in one direction, and the other overrunning clutch is adapted for torque delivery in the opposite direction. Each of the overrunning clutches includes an outer race that is adapted to be connected to the torque input elements of the gearing associated with that clutch through a selectively engageable friction clutch.
One of the overrunning clutches is adapted for torque delivery in a forward driving direction when the planetary gearing is conditioned for operation in each of the first two forward driving speed ratios. The other overrunning clutch is adapted for torque delivery during operation in a third forward driving direction. On a ratio shift from the third speed ratio to the fourth speed ratio, which is an overdrive ratio, it is necessary to disengage the friction clutch associated with the first overrunning clutch and to synchronously engage a brake for a reaction gear element of the planetary gearing.
This clutch and brake arrangement makes it necessary to provide two friction members as well as two overrunning clutches for controlling ratio changes between the fourth ratio and the third ratio. Each friction member requires added space in an environment in which space availability is a premium.
The need for two friction members (i.e., the friction clutch and the friction brake) associated with the first overrunning clutch complicates the design and makes it necessary to use synchronous control elements to effect engagement and release of the clutches and brakes in timed relationship during a ratio change between the fourth ratio and the third ratio.